Apache is such a monster of an application and can be configured in so many ways that it's not always easy to see how things are working. When I come across a configuration option I haven't worked with before, this book does a great job of explaining it in a language I can understand. It always starts off by saying _WHY_ you'd want to use a particular option, and is clear about pointing out when it might be better to use a different methodology.
The chapter on content negotiation is particularly good, and made me a huge fan of ModRewrite. I was looking for a simple way to serve up dynamic PHP CGI content through URLs that looked static (so search engines could easily spider the whole site). This chapter outlined many different approaches to this sort of task and carefully weighed the trade offs inherent in each. After reading it I felt that I had made an informed decision based on the particular needs and constraints of that project.
As with any printed book about web technologies, some of it may be out of date. Note that the author has written a newer book on Apache 2.0 which probably has more recent information regarding related technologies like PHP, Perl, etc. Still, there's going to be a lot of 1.X servers out there for quite a while so this book probably won't be collecting dust on my shelf anytime soon...
Now I think I'll buy his book on Apache 2.0
Peter Wainwright's book provides web server administrators and ISPs with the information they need to apply Apache to real world problems, using real examples, without bogging them down in excessive detail about every configuration directive.The key theme is 'Apache the way you want it' - through extensive examples, this book gives you the information you need to build, configure and extend Apache to suit your requirements.